The study, published in the academic journal Public Opinion
Quarterly in December, suggests that the images could have been
intended to tap into possible racial biases of some viewers.

"Ads that portray black candidates with a darker complexion might
prime negative stereotypes about blacks, damaging the candidate’s
election prospects in a way that has nothing to do with political
fitness for office and is difficult to detect," the researchers
wrote in the study.

In the GOP field, where real-estate mogul and current
front-runner, Donald Trump has consistently led in the polls, the
candidate's controversial approach to matters of
immigration,
homeland security, and
civil rights has relied on similar methods for attacking
minority groups.

In 2008, the depictions of Obama's skin tone varied throughout
the campaign season, but he appeared especially dark-skinned in
Republican attack ads that aired closer to election day,
according to the Stanford study.

Meanwhile, McCain's skin appeared gradually lighter over time in
the same ads.

The disparity in skin tone is not necessarily a result of
deliberate manipulation by the McCain campaign. The researchers
noted that "more shadowed" images of Obama may have been selected
to match the sinister tone of the attack ads.

According to the study, Obama's skin appeared the darkest in ads
connecting him to crime, including ones that attempted to link
the candidate to Bill Ayers, the former leader of the radical
left-wing organization Weather Underground:

Another ad sought to tie Obama to alleged misconduct committed by
the Association of Community Organizations for Reform Now, known
by the acronym ACORN:

Other GOP attack ads in question paint Obama as disrespectful ...

... and irresponsible ...

In another portion of the study, researchers showed participants
images that depicted Obama with a lighter or darker-than-usual
skin tone. The images were manipulated accordingly for the
purposes of the study.

The researchers found participants were quicker to think of
negative black stereotypes — such as laziness and criminal
behavior, for example — after seeing the darker-skinned version.

The findings give new ammunition to critics who claim the
Republican Party may use implicit racial appeals to attract some
voters.

Manipulated
images of Barack Obama that were used by researchers in the
study.Public Opinion
Quarterly

"When you blacken somebody's skin, you're doing it for only one
reason. It's to make them look darker and more sinister," First
Amendment attorney Daniel Barr
told Arizona's KTVK-3 TV.